We propose to use radionuclear and electrocardiograhic techniques to study the effects of coronary artery bypass surgery on left ventricular performance. We will employ radionuclide ventriculography at rest and exercise before and after coronary artery bypass surgery to examine changes in left ventricular function. We will examine Thallium myocardial perfusion Scintigraphy in the same patients to assess its usefulness compared to radionuclide ventriculography, and we will compare both techniques to conventional exercise electrocardiography for the detection of myocardial ischemia. We will employ a validated, rapid, semi-automatic border recognition algorithm for defining the left ventricular region of interest and automatically selecting a pericardiac background region of interest.